Input Device

ABSTRACT

An input device comprises a capacitive proximity and pressure sensor, which includes a first carrier layer, a second carrier layer and a spacer arranged between the first and second carrier layers, the first carrier layer having a first capacitor electrode applied thereon, the second carrier layer having a second capacitor electrode applied thereon, the first and second capacitor electrodes being arranged opposite one another with respect to the spacer in such a way that, in response to a compressive force acting on the pressure sensor, the first and second capacitor electrodes are brought closer together. The input device further comprises a control circuit configured so as to operate in at least two modes of operation, including a first and a second mode of operation. The control circuit determines, while in the first mode of operation, a quantity indicative of a capacitance between the first capacitor electrode and ground and, while in the second mode of operation, a quantity indicative of a capacitance between the first capacitor electrode and the second capacitor electrode.

TECHNICAL FIELD

This invention relates to input devices and more particularly to datainput devices including a film-based pressure sensor for human-applianceinteraction.

BACKGROUND ART

Input devices are commonly used in conjunction with electronicappliances to feed the latter with various kinds of inputs, includinge.g. control data influencing directly or indirectly the behavior of theappliance, input that is processed by the appliance and/or input that issimply stored.

It is known to construct input devices based upon film-type pressuresensors, whose resistance varies with pressure. Such film-type pressuresensor comprises two carrier films, which are arranged at a certaindistance from one another by means of a spacer. The spacer is providedwith at least one opening that defines an active zone of the sensor, inwhich the two carrier films face one another. Inside this active zone,at least two electrodes are arranged on the carrier films, in such a waythat electrical contact is established between the electrodes when thetwo carrier films are pressed together under the action of a compressiveforce acting on the sensor in the active zone. The pressure acting onthe sensor is detected and/or determined as a function of the resistancebetween the electrodes.

Depending on the application of such a pressure sensor, a layer ofsemiconducting material may be disposed between the electrodes, so thatthe sensor shows a gradual pressure sensitive behavior, that is to sayits resistance varies gradually or even continuously as a function ofthe force applied. The layer of semiconducting material may comprise amaterial whose internal electrical resistance varies as a function ofcompression or of deformation of the layer or a material whose surfacestructure confers to the layer a surface resistance that is reducedfollowing an increase in the number of points of contact with aconducting surface of an electrode, against which the layer ofsemiconducting material is pressed under the action of the compressiveforce.

WO 2004/049364 relates to a data input device comprising several keysarranged in at least two rows. A unidirectional position detector offilm-type construction is associated with each row of keys. Eachunidirectional position sensor enables the detection of the actuated keyalong the direction of the unidirectional position detector. Theunidirectional position sensors are interconnected in such a way that acontrol circuit can detect in which row a key has been actuated.

A different kind of sensors is based upon capacitive sensing. U.S. Pat.No. 3,896,425 discloses an electrical proximity detector that senses thechanges in the contents of a defined sensitive volume. The detectorcomprises an antenna that is driven by an oscillator and that emits anelectric field into the sensitive volume. A person or an objectintruding into the sensitive volume causes a change of the electricfield of the antenna, which is detected by the detector. To shape theelectric field of the antenna the detector comprises a first shield,driven by the oscillator with a signal of same amplitude and phase asthe signal of the antenna, and a second, grounded shield.

Other sensors based on electric field or “capacitive” sensing have beenproposed by J. Smith et al. in “Electric Field Sensing for GraphicalInterfaces”, IEEE Computer Graphics and Applications, Issue May/June1998, 54-60, as a human-computer interface. The interfaces are basedupon an array of electrodes to detect the gestures of a user.

The above-mentioned documents are herewith included herein by reference.

SUMMARY OF THE INVENTION

The invention provides an improved input device.

According to a first aspect of the invention, an input device comprisesa capacitive proximity and pressure sensor, which includes a firstcarrier layer, a second carrier layer and a spacer arranged between thefirst and second carrier layers, the first carrier layer having a firstcapacitor electrode applied thereon, the second carrier layer having asecond capacitor electrode applied thereon, the first and secondcapacitor electrodes being arranged opposite one another with respect tothe spacer in such a way that, in response to a compressive force actingon the pressure sensor, the first and second capacitor electrodes arebrought closer together. The input device further comprises a controlcircuit configured so as to operate in at least two modes of operation,including a first and a second mode of operation. The control circuitdetermines, while in the first mode of operation, a quantity indicativeof a capacitance between the first capacitor electrode and ground and,while in the second mode of operation, a quantity indicative of acapacitance between the first capacitor electrode and the secondcapacitor electrode. Those skilled will appreciate that the capacitancebetween the first capacitor electrode and ground is itself indicative ofthe proximity of a part of a user's body (e.g. their finger) to thefirst capacitor electrode. The first mode of operation therefore isconsidered as a “proximity-sensing” mode. On the other hand, thecapacitance between the first and the second capacitor electrode isindicative of the distance between these electrodes. Since a givendistance corresponds to a certain amount of pressure or magnitude offorce, the second mode of operation is considered as a“pressure-sensing” (or “force-sensing”) mode.

According to a second aspect of the invention, the input devicecomprises a capacitive proximity and pressure sensor, which includes afirst carrier layer, a second carrier layer and a spacer arrangedbetween the first and second carrier layers. The first carrier layer hasa plurality of first capacitor electrodes applied thereon and the secondcarrier layer has a plurality of second capacitor electrodes appliedthereon, each one of the plurality of first capacitor electrodes beingarranged opposite a respective one of the plurality of second capacitorelectrodes with respect to the spacer in such a way that, in response toa compressive force acting on the pressure sensor, respectively oppositeones of the first and second capacitor electrodes are brought closertogether. The input device according to the second aspect furthercomprises a control circuit configured so as to operate in at least twomodes of operation, including a first and a second mode of operation.The control circuit determines, while in the first (proximity-sensing)mode of operation, a quantity indicative of a capacitance betweenindividual ones (single ones or groups) of the plurality of firstcapacitor electrodes and ground and, while in the second(pressure-sensing) mode of operation, a quantity indicative of acapacitance between individual ones of the plurality of first capacitorelectrodes and the respectively opposite ones of the plurality of secondcapacitor electrodes.

According to a third aspect of the invention, the input device comprisesa capacitive proximity and pressure sensor, which includes a firstcarrier layer, a second carrier layer and a spacer arranged between thefirst and second carrier layers. The first carrier layer has a pluralityof first elongated capacitor electrodes applied thereon and the secondcarrier layer has a plurality of second elongated capacitor electrodesapplied thereon, the plurality of first capacitor electrodes beingarranged opposite the plurality of second capacitor electrodes withrespect to the spacer. According to the present aspect, the firstelongated capacitor electrodes extend transversally to the secondelongated capacitor electrodes in such a way that, in response to acompressive force acting locally on the pressure sensor, opposite onesof the first and second capacitor electrodes are brought closer togetherat the location where the compressive force acts on the pressure sensor.The input device also comprises a control circuit, which determines,while in a first mode of operation, a quantity indicative of capacitancebetween individual ones of the plurality of first capacitor electrodesand ground and, while in a second mode of operation, a quantityindicative of a capacitance between individual ones of the plurality offirst capacitor electrodes and individual ones of the plurality ofsecond capacitor electrodes.

According to a fourth aspect of the invention, the input devicecomprises a capacitive proximity and pressure sensor, which includes afirst carrier layer, a second carrier layer and a spacer arrangedbetween the first and second carrier layers for keeping the first andsecond carrier layers apart from one another. The first carrier layerhas a plurality of first capacitor electrodes applied thereon, thesecond carrier layer has a second capacitor electrode applied thereon,the plurality of first capacitor electrodes being arranged opposite thesecond capacitor electrode with respect to the spacer in such a waythat, in response to a compressive force acting locally on the pressuresensor, individual ones of the first capacitor electrodes are broughtcloser to the second capacitor electrode at the location where thecompressive force acts on the pressure sensor. The input deviceaccording to the fourth aspect comprises a control circuit, whichdetermines, while in a first mode of operation, a quantity indicative ofcapacitance between individual ones of the first capacitor electrodesand ground and, while in a second mode of operation, a quantityindicative of a capacitance between the second capacitor electrode andindividual ones of the first capacitor electrodes.

For the purposes of the present, the terms “first mode of operation” and“second mode of operation” are primarily used for distinguishing themodes of operation; these terms therefore should not be understood asindicating an order of the modes of operation in time. The controlcircuit may operate in the first mode of operation before and/or afteroperating in the second mode of operation. The control circuit maycyclically switch between the modes of operation, e.g. several times persecond. Preferably, however, the control circuit remains in theproximity-sensing mode (first mode) until the proximity of a body havingan electric-field-changing property is detected. Alternatively, thecontrol circuit could remain in the pressure-sensing mode (second mode)until a force or pressure exceeding a predefined threshold has beendetected.

For the purposes of the present, a “quantity indicative of acapacitance” can be any physical quantity that is linked to thecapacitance by the laws of physics, such as, for instance, amplitudeand/or phase of a current, amplitude and/or phase of a voltage, charge,impedance, etc.

According to a preferred embodiment of the input devices as recitedhereinabove, the spacer is electrically insulating and compressible.According to this embodiment, opposite ones of the first and secondcapacitor electrodes are brought closer together when the spacer iscompressed in response to a compressive force acting on the pressuresensor.

According to another preferred embodiment of the input device as recitedhereinabove, the spacer has one or more openings therein, with respectto which the first capacitor electrode or electrodes are arrangedopposite the second capacitor electrode or electrodes. The firstcapacitive electrode(s) and/or the second capacitor electrode(s) have aninsulating layer or insulating pattern arranged thereon in such a way asto prevent a short circuit between the first capacitive electrode(s) andthe second capacitor electrode(s). The insulating layer or pattern couldbe separate from the spacer or part of it (in the latter case theopening would rather be considered as a recess than as a through-hole).The spacer may be compressible or incompressible. In the latter case,the first and second capacitor electrodes are brought closer togetherwhen one or both of the carrier layers bend into the opening(s) of thespacer under the action of the compressive force.

If the spacer has a plurality of openings therein, if the first carrierlayer has a plurality of first capacitor electrodes applied thereon andif the second carrier layer has a plurality of second capacitorelectrodes applied thereon, each one of the plurality of first capacitorelectrodes is preferably arranged opposite a respective one of theplurality of second capacitor electrodes with respect to a respectiveone of the plurality of openings. In this case, when a compressive forceacts on the pressure sensor, respectively opposite ones of the first andsecond capacitor electrodes are brought closer together.

Those skilled will appreciate that various options exist for determininga quantity indicative of capacitance between the first capacitorelectrode(s) and ground. For instance, the control circuit coulddetermine, while in the first mode of operation,

-   (a) an amount of electric charge accumulated on (individual ones of)    the first capacitor electrode(s) in response to applying a defined    voltage to this (these) first capacitor electrode(s); or-   (b) an amplitude and/or a phase of a loading current flowing in    (individual ones of) the first capacitor electrode(s) in response to    applying an oscillating voltage to this (these) first capacitor    electrode(s); or-   (c) an in-phase component and/or a 90°-phase-offset component of a    loading current flowing in (individual ones of) the first capacitor    electrode(s) in response to applying an oscillating voltage to this    (these) first capacitor electrode(s); or-   (d) a charge time and/or a discharge time of (individual ones of)    the first capacitor electrode(s).

Similarly, various options exist for determining a quantity indicativeof capacitance between (individual ones of) the first capacitorelectrode(s) and (individual ones of) the second capacitor electrode(s).For instance, the control circuit could determine, while in the secondmode of operation,

-   (a) an amount of electric charge accumulated on (individual ones of)    the first capacitor electrode(s) and/or (on individual ones of) the    second capacitor electrode(s) in response to an applying a defined    voltage to the respectively opposite capacitor electrode(s);-   (b) an amount of electric charge accumulated on (individual ones of)    the first capacitor electrode(s) and/or (on individual ones of) the    second capacitor electrode(s) in response to an applying a defined    voltage to this (these) capacitor electrode(s);-   (c) an amplitude and/or a phase of a loading current flowing (in    individual ones of) the first capacitor electrode(s) in response to    applying an oscillating voltage to this (these) first capacitor    electrode(s);-   (d) an amplitude and/or a phase of a loading current flowing (in    individual ones of) the second capacitor electrode(s) in response to    applying an oscillating voltage to this (these) second capacitor    electrode(s);-   (e) an amplitude and/or a phase of a loading current flowing (in    individual ones of) the first capacitor electrode(s) in response to    applying an oscillating voltage to the respectively opposite one(s)    (of the) second capacitor electrode(s);-   (f) an amplitude and/or a phase of a loading current flowing (in    individual ones of) the second capacitor electrode(s) in response to    applying an oscillating voltage to the respectively opposite one(s)    (of the) first capacitor electrode(s);-   (g) an in-phase component and/or a 90°-phase-offset component of a    loading current flowing (in individual ones of) the first capacitor    electrode(s) in response to applying an oscillating voltage to this    (these) first capacitor electrode(s);-   (h) an in-phase component and/or a 90°-phase-offset component of a    loading current flowing (in individual ones of) the second capacitor    electrode(s) in response to applying an oscillating voltage to this    (these) second capacitor electrode(s);-   (i) an in-phase component and/or a 90°-phase-offset component of a    coupling current flowing (in individual ones of) the first capacitor    electrode(s) in response to applying an oscillating voltage to the    respectively opposite one(s) (of the) second capacitor electrode(s);-   (j) an in-phase component and/or a 90°-phase-offset component of a    coupling current flowing (in individual ones of) the second    capacitor electrode(s) in response to applying an oscillating    voltage to the respectively opposite one(s) (of the) first capacitor    electrode(s);-   (k) a charge and/or a discharge time of the first and/or the second    capacitor electrode.

While in the first mode of operation, the control circuit preferablyapplies a first voltage to the first electrode(s) and a second voltageto the second electrode(s), the first and second voltages having sameamplitude and phase. As will be appreciated, this substantially cancelsthe electric field between the first and second capacitor electrodes sothat the first capacitor electrode(s) becomes (become) substantiallyinsensitive in direction of the second capacitor electrode(s).

According to a preferred embodiment of the input device, the firstcarrier layer, the spacer and the second carrier layer are laminatedtogether.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details and advantages of the present invention will be apparentfrom the following detailed description of several not limitingembodiments with reference to the attached drawings, wherein:

FIG. 1 is a schematic cross sectional view of capacitive pressure andproximity sensor according to a first embodiment;

FIG. 2 is a schematic cross sectional view of an input device accordingto a second embodiment;

FIG. 3 is an illustration of different examples of electricallyinsulating patterns;

FIGS. 4 a and 4 b are cross sectional views of a touchpad having keypadfunctionality;

FIGS. 5 a and 5 b are cross sectional views of an alternative touchpadhaving keypad functionality;

FIGS. 6 a and 6 b are cross sectional views of yet another example of atouchpad having keypad functionality;

FIGS. 7 a-7 c are illustrations of a touchpad with keypad functionality,in which the keys are arranged along a straight line;

FIGS. 8 a-8 e are illustrations of an input device implemented as alinear slider;

FIGS. 9 a-9 d are illustrations of an input device implemented as acircular slider;

FIGS. 10 a-10 d are illustrations of variants of an alternativeembodiment of a touchpad;

FIGS. 11 a-11 b are cross-sectional schematic views of yet anotherexample of an input device.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a data input device 10, comprising a capacitive proximityand pressure sensor 12 of film-type construction. The capacitiveproximity and pressure sensor 12 comprises first and second carrierlayers in the form of the first and second carrier films 16, 18, made ofsubstantially flexible, electrically insulating material, such as e.g.PET, PEN, PI or the like. A spacer 20 is sandwiched between the firstand second carrier films 16, 18 so as to keep them apart from oneanother. The spacer 20 is also be made of a substantially flexible,electrically insulating material, e.g. a double-sided adhesive. Thespacer 20 is provided with an opening 14 therein, which delimits anactive zone of the pressure sensor 10. In the active zone 14, the firstcarrier foil 16 carries a first capacitor electrode 22 on the sidedirected towards the second carrier film 18, while the second carrierfoil 18 carries a second capacitor electrode 24 on the side directedtowards the first carrier film 16. The first and second capacitorelectrodes 22, 24 are formed from conductive material (e.g. silver ink)applied directly on the first and second carrier films 16, 18,respectively. The second capacitor electrode has formed thereon a layer26 of electrically insulating material (dielectric, e.g. PET, PEN, PI,etc.).

The right-hand side of FIG. 1 shows a control circuit 28 connected tothe first and second capacitor electrodes 22, 24 by leads 30, 32. Thecontrol circuit 28 comprises a microprocessor, an application-specificintegrated circuit (ASIC) or a programmable chip, configured so as tooperate in at least a first and a second mode of operation. The controlcircuit determines, while in the first mode of operation, a quantityindicative of a capacitance between the first capacitor electrode andground and, while in the second mode of operation, a quantity indicativeof a capacitance between the first capacitor electrode and the secondcapacitor electrode.

The first mode of operation is associated to sensing the proximity of anobject to be sensed, e.g. of a user's finger 34. In the first mode ofoperation the control circuit keeps the first and second electrodesessentially at the same electric potential so that the electric fieldsubstantially cancels between the first and second electrodes. Thesecond electrode 24 thus acts as a driven shield for the first electrode22 and the sensitivity of the latter is directed away from the secondelectrode 24. If an oscillating voltage is applied to the firstcapacitor electrode an oscillating electric field to ground is built up.The object to be sensed modifies the capacitance between the firstcapacitor electrode and ground, which is sensed by the control circuit28. It should be noted that in the first mode of operation detecting theproximity of the object to be does not require the object touching orbeing in contact with the proximity and pressure sensor 12.

The second mode of operation is associated with sensing pressure exertedon the sensor by some kind of actuator, such as e.g. the user's fingeror stylus. In the second mode of operation, the control circuitessentially determines the capacitance of the capacitor formed by thefirst and the second capacitor electrodes 22, 24. It is well known thatthe capacitance of a capacitor depends upon the distance between itselectrodes. In the illustrated case, the distance between the first andsecond capacitor electrodes decreases with increasing pressure exertedupon the pressure sensor by the user. As a consequence, the capacitancebetween the capacitor electrodes increases, which is detected by thecontrol circuit 28.

FIG. 2 shows a variant of the proximity and pressure sensor of FIG. 1.The construction is the same, except that the first capacitor electrode22, like the second capacitor electrode 24, has formed thereon a layer26 of electrically insulating material. Those skilled will appreciatethat patterning one of the electrically insulating layers 26 allowstailoring the response of the proximity and pressure sensor in thesecond mode of operation. As long as the electrically insulating layersare spaced from one another (i.e. for low pressures exerted by the user)the pattern has no significant influence on sensor response. However, asthe pressure increases the electrically insulating layers come intocontact and a contact surface forms. A patterned insulating layerresults in that the minimum distance between the first and secondelectrodes is varying on the contact surface. Accordingly, thecapacitance increase is different from the case where the insulatinglayers are uniform. Examples of patterned insulating layers are shown inFIG. 3.

In FIGS. 4 a-4 b, elements similar to elements of FIG. 1 have beenattributed the same reference numeral as the corresponding element ofFIGS. 1 and 2, preceded by a prefix according to the number of thedrawing.

FIGS. 4 a and 4 b show a cross section of a touchpad 412 having keypadfunctionality. The touchpad 412 comprises a laminated structure of afirst carrier film 416, a second carrier film 418 and a spacer 420,sandwiched between the first and second carrier films so as to keep themspaced apart. The spacer 420 has a matrix-like arrangement of openings414 therein, which define keys of the touchpad 412. To each key isassociated a pair of a first capacitor electrode 422 and a secondcapacitor electrode 424 arranged on the first and second carrier films416, 418, respectively. Each first capacitor electrode 422 is arrangedopposite its second-capacitor-electrode counterpart 424, with respect tothe associated opening 414 of the spacer 420. The touchpad 412 furthercomprises a control circuit (not shown, for the sake of clarity of thedrawings), which determines, in a first mode of operation, a quantityindicative of capacitance between individual ones of the first capacitorelectrodes 422 and ground and, in a second mode of operation, a quantityindicative of a capacitance between individual ones of the firstcapacitor electrodes 422 and the associated ones of the second capacitorelectrodes 424.

In FIG. 4 a, a user's finger 434 lightly touches the first carrier film416. The force exerted is not sufficient to cause significant bending ofthe first carrier film 416 in the region of a key. The position of theuser's finger 434 is detected by determining, for each one of the firstcapacitor electrodes 422, the quantity indicative of capacitive couplingbetween this electrode 422 and ground. The position may e.g. be computedas the centroid of the positions of the first capacitor electrodes 422,weighed with the corresponding quantity indicative of capacitance. Thefirst mode of operation is suitable, for instance, when the usercontrols a cursor (e.g. on the display of an appliance) with thetouchpad 412.

In FIG. 4 b, the user presses down the first carrier film 416, so thatit bends into an opening 414 of the spacer 420 and the distance betweenthe corresponding first and second capacitor electrodes 422, 424decreases. This causes the capacitance between these capacitorelectrodes to go up, which can be detected in the second mode ofoperation of the touchpad 412. The second mode of operation is,therefore, associated to actuation of a key of the touchpad 412, e.g. bya user's finger 434 or a stylus.

In operation, the first and second modes of operation are carried out inalternance, i.e. the touchpad 412 is switched, more or lessperiodically, from the first mode of operation to the second mode andinversely. It should be noted that, in the second mode of operation, thetouchpad does not need to determine the quantity indicative ofcapacitance for each key. Indeed, it is considered advantageous if thelatter is determined only with respect to that key or those keys in theneighborhood of which the position of the user's finger 434 has beendetected when the touchpad 412 operated in the first mode of operation.

FIGS. 5 a and 5 b show a cross section of an alternative touchpad 512having keypad functionality. The touchpad 512 comprises a first carrierfilm 516, a second carrier film 518 and a spacer 521, sandwiched betweenthe first and second carrier films 516, 518 so as to keep them spacedapart. The spacer 521 is made of an electrically insulating,compressible foam material, e.g. polyurethane foam or the like. Thefirst and second carried films 516, 518 have capacitor electrodes 522,524 applied on the surfaces that face the spacer 521. Each firstcapacitor electrode 522 is arranged on the first carrier film opposite asecond capacitor electrode 524 on the second carrier film, with respectto the spacer 521. Each pair of opposite first and second capacitorelectrodes defines a key of the touchpad 512. The latter furthercomprises a control circuit (not shown), which determines, in a firstmode of operation, a quantity indicative of capacitance betweenindividual ones of the first capacitor electrodes 522 and ground and, ina second mode of operation, a quantity indicative of a capacitancebetween individual ones of the first capacitor electrodes 522 and theassociated ones of the second capacitor electrodes 524.

In FIG. 5 a, a user's finger 534 lightly touches the first carrier film516. The force exerted is not sufficient to cause significant bending ofthe first carrier film 516 in the region of a key. The position of theuser's finger 534 is detected by determining, for each one of the firstcapacitor electrodes 522, the quantity indicative of capacitive couplingbetween this electrode 522 and ground. As in the previous example, theposition may e.g. be computed as the centroid of the positions of thefirst capacitor electrodes 522, weighed with the corresponding quantityindicative of capacitance. The first mode of operation is suitable, forinstance, when the user controls a cursor (e.g. on the display of anappliance) with the touchpad 512.

In FIG. 5 b, the user presses on the first carrier film 516, so that theunderlying spacer 521 is compressed, whereby the distance between a pairof first and second capacitor electrodes 522, 524 decreases. This causesthe capacitance between these capacitor electrodes to go up, which canbe detected in the second mode of operation of the touchpad 512. Thesecond mode of operation is, therefore, associated to actuation of a keyof the touchpad 512, e.g. by a user's finger 534 or a stylus.

Operation of the touchpad 512 is similar to the previous example: thefirst and second modes of operation are carried out in alternance, i.e.the touchpad 512 is switched, more or less periodically, from the firstmode of operation to the second mode and inversely. In the second modeof operation, it is considered advantageous if the quantity indicativeof capacitance between a first and a second capacitor electrode 522, 524is determined only with respect to that key or those keys in theneighborhood of which the position of the user's finger 534 has beendetected when the touchpad 512 operated in the first mode of operation.

FIGS. 6 a and 6 b illustrate that it is also possible to combine theembodiments of the preceding examples within a single touchpad. Thetouchpad 612 comprises a first carrier film 616, a second carrier film618 and a first spacer 620, sandwiched between the first and secondcarrier films 616, 618 so as to keep them spaced apart. The spacer 620has a matrix-like arrangement of openings 614 therein, which define keysof the touchpad 612. To each key is associated a pair of a firstcapacitor electrode 622 and a second capacitor electrode 624 arranged onthe first and second carrier films 616, 618, respectively. Each firstcapacitor electrode 622 is arranged opposite itssecond-capacitor-electrode counterpart 624, with respect to theassociated opening 614 of the spacer 620. Some of the openings (middlekeys in FIGS. 6 a and 6 b) in spacer 620 are filled with electricallyinsulating, compressible foam material 621, e.g. polyurethane foam orthe like. The spacer 620 is made, in this example, from a flexiblematerial, which has substantially lower compressibility than the foammaterial 621. The haptic properties of keys with foam material 621differ from those without the foam material. Similarly, theircapacitance as a function of pressure behaves differently. Nevertheless,operation of touchpad 621 is analogous to operation of touchpads 412 and512.

FIGS. 7 a-7 c show a touchpad 712 with keypad functionality, in whichthe keys are arranged along a straight line (a curve would also befeasible). FIG. 7 a shows the layout of the keys, FIGS. 7 b and 7 c showcross-sectional views of the touchpad 712. The touchpad 712 comprises alaminated structure of a first carrier film 716, a second carrier film718 and a spacer 720, sandwiched between the first and second carrierfilms so as to keep them spaced apart. The spacer 720 has openings 714therein, which are arranged along a line and which define the keys ofthe touchpad 712. To each key is associated a first capacitor electrode722 arranged on the first carrier film 716. A common second capacitorelectrode 724 extends over all the keys of the touchpad 712. Thetouchpad 712 further comprises a control circuit (not shown), whichdetermines, in a first mode of operation, a quantity indicative ofcapacitance between individual ones of the first capacitor electrodes722 and ground and, in a second mode of operation, a quantity indicativeof a capacitance between individual ones of the first capacitorelectrodes 722 and the common second capacitor electrode 724.

In FIG. 7 b, a user's finger 734 lightly touches the first carrier film716. The force exerted is not sufficient to cause significant bending ofthe first carrier film 716 in the region of a key. The position of theuser's finger 734 is detected by determining, for each one of the firstcapacitor electrodes 722, the quantity indicative of capacitive couplingbetween this electrode 722 and ground. The position may e.g. be computedas the centroid of the positions of the first capacitor electrodes 722,weighed with the corresponding quantity indicative of capacitance. Thefirst mode of operation is suitable, for instance, when the usercontrols a cursor (e.g. on the display of an appliance) with thetouchpad 712.

In FIG. 7 c, the user presses down the first carrier film 716, so thatit bends into an opening 714 of the spacer 720 and the distance betweenthe corresponding first electrode 722 and the second capacitor electrode724 decreases. This causes the capacitance between these capacitorelectrodes to go up, which can be detected in the second mode ofoperation of the touchpad 712. The second mode of operation is,therefore, associated to actuation of a key of the touchpad 712, e.g. bya user's finger 734 or a stylus.

In operation, the first and second modes of operation are carried out inalternance, i.e. the touchpad 712 is switched, more or lessperiodically, from the first mode of operation to the second mode andinversely. It should be noted that, in the second mode of operation, thetouchpad does not need to determine the quantity indicative ofcapacitance for each key. Indeed, it is considered advantageous if thelatter is determined only with respect to that key or those keys in theneighborhood of which the position of the user's finger 734 has beendetected when the touchpad 712 operated in the first mode of operation.

FIGS. 8 a-8 c show possible layouts of a slider 812, FIGS. 8 d and 8 eshow cross-sectional views thereof. The slider 812 comprises a laminatedstructure of a first carrier film 816, a second carrier film 818 and aspacer 820, sandwiched between the first and second carrier films so asto keep them spaced apart. The spacer 820 has an opening 814 therein,which extends, in this case, along a straight line (a curvilinear courseis possible, see FIGS. 9 a-9 d). The opening 814 defines the active zoneof the slider 812. The first carrier film 816 has first capacitorelectrodes arranged thereon in the active zone, the second carrier filmhas a common second capacitor electrode 824 applied thereon in theactive zone. The first capacitor electrodes 822 are arranged in facingrelationship to the second capacitor electrode 824. The second capacitorelectrode has a thin dielectric layer 826 arranged thereon, whichprevents short-circuits between the first capacitor electrodes 822 andthe second capacitor electrode 824, if they are brought closer to oneanother by a compressive force acting on the slider 812.

In FIG. 8 d, a user's finger 834 lightly touches the first carrier film816. The force exerted is not sufficient to cause significant bending ofthe first carrier film 816 in the region of the active zone. In FIG. 8e, however, the user presses down the first carrier film 816, so that itlocally bends into the opening 814 of the spacer 820 and the distancebetween the first electrodes 822 and the second capacitor electrode 824decreases at the point where the force is applied.

In the sliders of FIGS. 8 a and 8 b, the first capacitor electrodes 822are separately connected to a control circuit (not shown). Accordingly,these sliders are able to detect the position of the user's finger 834(in the first and the second mode of operation). In the first mode ofoperation, the control circuit determines, for each one of the firstcapacitor electrodes 822, the quantity indicative of capacitive couplingbetween this electrode 822 and ground. The said position may e.g. becomputed as the centroid of the positions of the first capacitorelectrodes 822, weighed with the corresponding quantity indicative ofcapacitance. In the second mode of operation, a quantity indicative of acapacitance between single ones of the first capacitor electrodes 822and the common second capacitor electrode 824 can be detected. As can beseen, operation of the slider 812 as shown in FIGS. 8 a and 8 b issimilar to operation of the keypad 712.

In the slider of FIG. 8 c, the first capacitor electrodes are notseparately connected to the control circuit. Instead, there are threegroups of first capacitor electrodes 822. The first capacitor electrodes822 of each group are conductively interconnected. Along the activezone, a first capacitor electrode of the first group is followed by oneof the second group, which is, in turn, followed by one of the thirdgroup, after which the succession starts again with a first capacitorelectrode of the first group. A slider as shown in FIG. 8 c is notcapable of detecting (absolute) position of the user's finger 834 orstylus. Nevertheless, such slider can detect movement of the user'sfinger 834 or stylus (in both modes of operation). In the first mode ofoperation, when the user's finger 834 moves from the left to the right,the succession of the groups of first capacitor electrodes that haveincreased capacitive coupling to ground is 2-3-1 (and cyclicallycontinued). When the user's finger 834 moves from the right to the left,the succession of the groups of first capacitor electrodes that haveincreased capacitive coupling to ground is 3-2-1 (and cyclicallycontinued). In the second mode of operation, the direction of movementcan be determined from the succession of the groups of first capacitorelectrodes that have increased capacitive coupling to the secondcapacitor electrode. Of course, in the second mode of operation, theamount of force exerted upon the slider can also be detected. Forinstance, if the quantity indicative of capacitance exceeds apredetermined threshold, some switching action may be triggered.

Given the reduced number of external connectors, the slider of FIG. 8 cis particularly interesting if the absolute position needs not to beknown, e.g. for navigating though list-based menus (scrolling through alist of items displayed and selecting an item to enter a sub-menu orstart a certain function). The action of selecting an item from the listcan e.g. take place when the user presses on the slider with a forcethat causes the quantity indicative of capacitance between the first andsecond capacitor electrodes to exceed the predetermined threshold.

FIGS. 9 a-9 d show circular sliders 912. The sliders of FIGS. 9 a and 9b are configured for detecting position (sliders with keypadfunctionality); those of FIGS. 9 c and 9 d are analogous to the linearslider of FIG. 8 c.

FIGS. 10 a-10 c show schematic top views, FIG. 10 d a schematiccross-sectional view of variants of an alternative embodiment of atouchpad 1012. The touchpad 1012 has a plurality of first elongatedcapacitor electrodes 1022 applied on the first carrier film 1016 and aplurality of second elongated capacitor electrodes 1024 applied on thesecond carrier films 1018. The first capacitor electrodes 1022 arearranged opposite the second capacitor electrodes with respect to anopening 1014 in spacer 1020, which is sandwiched between the carrierfilms 1016, 1018. The first capacitor electrodes 1022 extend crosswiseto the second capacitor electrodes 1024. In the shown embodiment, theangle between any one of the first capacitor electrodes and any one ofthe second capacitor electrodes is 90°; it should, however, be notedthat this angle could also be different from 90°, e.g. between 30° and90°. The second capacitor electrodes 1024 are covered with a thindielectric layer, which prevent a short-circuit when the first andsecond capacitor electrodes 1022, 1024 are brought closer together atthe location where a compressive force acts on the touchpad 1012. Thetouchpad 1012 is connected to control circuit (not shown), whichdetermines, while in the first mode of operation, a quantity indicativeof capacitance between individual ones of the first capacitor electrodes1022 and ground and, while in the second mode of operation, a quantityindicative of a capacitance between individual ones of the firstcapacitor electrodes 1022 and individual ones of the second capacitorelectrodes 1024.

In the touchpads of FIGS. 10 a and 10 b, the capacitor electrodes 1022and 1024 are separately connected to a control circuit (not shown).Accordingly, these touchpads are able to detect the position of theuser's finger 1034 (with respect to one dimension in the first mode ofoperation and with respect to two dimensions in the second mode ofoperation). In the first mode of operation, the control circuitdetermines, for each one of the first capacitor electrodes 1022, thequantity indicative of capacitive coupling between this electrode 1022and ground. The position may e.g. be computed as the centroid of thepositions of the first capacitor electrodes 1022, weighed with thecorresponding quantity indicative of capacitance. It should be notedthat in first mode of operation, the position of the user's finger 1034is detected in the direction perpendicular to the direction along whichthe first capacitor electrodes extend. In the second mode of operation,the control circuit determines, for each one of the first capacitorelectrodes 1022, the quantity indicative of capacitance between thiselectrode 1022 and each one of the second capacitor electrodes 1024. Theposition of the user's finger (the point of application of the force) isobtained from those first and second electrodes, which show maximumcapacitive coupling.

In FIG. 10 c, the first and the second capacitor electrodes 1022 and1024 are not separately connected to the control circuit. Instead, thereare three groups of first capacitor electrodes 1022 and three groups ofsecond capacitor electrodes 1024. The capacitor electrodes of each groupare conductively interconnected. Along the direction perpendicular tothe first capacitor electrodes, a first capacitor electrode of the firstgroup is followed by one of the second group, which is, in turn,followed by one of the third group, after which the succession startsagain with a first capacitor electrode of the first group. The secondcapacitor electrodes are arranged analogously. A touchpad as shown inFIG. 10 c is not capable of detecting (absolute) position of the user'sfinger 1034 or stylus. Nevertheless, such touchpad can detect movementof the user's finger 1034 or stylus. In the first mode of operation,when the user's finger 1034 moves perpendicular to the first capacitorelectrodes, the succession of the groups of first capacitor electrodeswhich have increased capacitive coupling to ground is 2-3-1 (andcyclically continued) or 3-2-1 (and cyclically continued), depending onthe direction of the movement. In the second mode of operation, thedirection of the movement perpendicular to the first capacitorelectrodes can be determined from the succession of the groups of firstcapacitor electrodes which have increased capacitive coupling to thesecond capacitor electrodes. Likewise, the direction of the movementperpendicular to the second capacitor electrodes can be determined fromthe succession of the groups of second capacitor electrodes which haveincreased capacitive coupling to the first capacitor electrodes. Ofcourse, in the second mode of operation, the amount of force exertedupon the touchpad can also be detected. For instance, if the quantityindicative of capacitance exceeds a predetermined threshold, someswitching action may be triggered.

FIGS. 11 a and 11 b show yet another alternative embodiment of an inputdevice including a proximity and pressure sensor 1112. The capacitiveproximity and pressure sensor 1112 comprises a first carrier layer inthe form of a substantially rigid cover 1116 and a second carrier layerin the form of a substrate 1118. The rigid cover 1116 includes aplurality of component layers, such as a protective hard plastic 1116 a,a double-sided adhesive 1116 b and a flexible thermoplastic film 1116 c.A pivot 1123 is sandwiched between the first and second carrier layers1116, 1118. The capacitive proximity and pressure sensor 1112 compriseselectrode pairs diametrically opposed with respect to the pivot 1123.Each electrode pair comprises a first capacitor electrode 1122 arrangedon the first carrier layer 1116 (on the side directed towards the secondcarrier layer 1118) and a second capacitor electrode 1124 on the secondcarrier layer 1118 (on the side directed towards the first carrier layer1116). The first and second capacitor electrodes 1122, 1124 are formedfrom conductive material (e.g. silver ink) applied directly on the firstand second carrier layers, respectively. A spacer 1121 made ofelectrically insulating foam material is arranged between the first andsecond capacitor electrodes of a pair.

The first and second capacitor electrodes 1122, 1124 are connected to acontrol circuit (not shown). The control circuit determines, while inthe first mode of operation, a quantity indicative of a capacitancebetween the first capacitor electrodes and ground and, while in thesecond mode of operation, a quantity indicative of a capacitance betweenthe first capacitor electrode and the second capacitor electrode of eachpair.

The first mode of operation is associated to sensing the proximity of anobject to be sensed, e.g. of a user's finger 1134. In the first mode ofoperation the control circuit keeps the first and second electrodesessentially at the same electric potential so that the electric fieldsubstantially cancels between the first and second electrodes. Thesecond electrodes 1124 thus act as driven shields for the respectivefirst electrodes 1122 and the sensitivity of the latter is directed awayfrom the respective second electrode 1124. If an oscillating voltage isapplied to the first capacitor electrode, an oscillating electric fieldto ground is built up. The object to be sensed modifies the capacitancebetween the first capacitor electrode and ground, which is sensed by thecontrol circuit 1128.

The second mode of operation is associated with sensing pressure exertedon the sensor by some kind of actuator, such as e.g. the user's finger1134 or stylus. In the second mode of operation, the control circuitessentially determines the capacitance of the capacitor formed by thefirst and the second capacitor electrodes 1122, 1124. In the embodimentof FIGS. 11 a and 11 b, pressure exerted on the proximity and pressuresensor 1112 by the user causes the first carrier layer to tilt, wherebythe first and second capacitor electrodes of a first pair get closertogether (right-hand side in FIG. 11 b) and those of a second pair aremoved away from one another (left-hand side in FIG. 11 b). When the userstops pressing on the sensor, the foam spacers 1121 bring the firstcarrier layer back into the neutral position.

1. An input device comprising a capacitive proximity and pressuresensor, including a first carrier layer, a second carrier layer and aspacer arranged between said first and second carrier layers, said firstcarrier layer having a first capacitor electrode applied thereon, saidsecond carrier layer having a second capacitor electrode appliedthereon, said first and second capacitor electrodes being arrangedopposite one another with respect to said spacer in such a way that, inresponse to a compressive force acting on the pressure sensor, the firstand second capacitor electrodes are brought closer together; and acontrol circuit configured so as to operate in at least a first and asecond mode of operation, said control circuit determining, while insaid first mode of operation, a quantity indicative of a capacitancebetween said first capacitor electrode and ground; and, while in saidsecond mode of operation, a quantity indicative of a capacitance betweensaid first capacitor electrode and said second capacitor electrode. 2.The input device as claimed in claim 1, wherein said spacer has anopening therein, said first and second capacitor electrodes beingarranged opposite one another with respect to said opening of thespacer, wherein said first and/or said second capacitor electrode has aninsulating layer or insulating pattern arranged thereon in such a way asto prevent a short circuit between said first and second capacitorelectrodes when said first and second capacitor electrodes are broughtcloser together.
 3. The input device as claimed in claim 1, wherein saidspacer is electrically insulating and compressible, and wherein saidfirst and second capacitor electrodes are brought closer together whensaid spacer is compressed in response to a compressive force acting onthe pressure sensor.
 4. The input device as claimed in claim 1, whereinsaid control circuit determines, while in said first mode of operation,an amount of electric charge accumulated on said first capacitorelectrode in response to applying a defined voltage to said firstcapacitor electrode.
 5. The input device as claimed in claim 1, whereinsaid control circuit determines, while in said first mode of operation,an amplitude and/or a phase of a loading current flowing in said firstcapacitor electrode in response to applying an oscillating voltage tosaid first capacitor electrode.
 6. The input device as claimed in claim1, wherein said control circuit determines, while in said first mode ofoperation, an in-phase component and/or a 90°-phase-offset component ofa loading current flowing in said first capacitor electrode in responseto applying an oscillating voltage to said first capacitor electrode. 7.The input device as claimed in claim 1, wherein said control circuitdetermines, while in said first mode of operation, a charge time and/ora discharge time of said first capacitor electrode.
 8. The input deviceas claimed in claim 1, wherein said control circuit, while in said firstmode of operation, applies a first voltage to said first electrode and asecond voltage to said second electrode, said first and second voltageshaving same amplitude and phase.
 9. The input device as claimed in claim1, wherein said control circuit determines, while in said second mode ofoperation, an amount of electric charge accumulated on one of said firstand second capacitor electrodes in response to an applying a definedvoltage to the other of said first and second capacitor electrodes. 10.The input device as claimed in claim 1, wherein said control circuitdetermines, while in said second mode of operation, an amount ofelectric charge accumulated on one of said first and second capacitorelectrodes in response to an applying a defined voltage to said one ofsaid first and second capacitor electrodes.
 11. The input device asclaimed in claim 1, wherein said control circuit determines, while insaid second mode of operation, an amplitude and/or a phase of a couplingcurrent flowing in one of said first and second capacitor electrodes inresponse to applying an oscillating voltage to the other of said firstand second capacitor electrodes.
 12. The input device as claimed inclaim 1, wherein said control circuit determines, while in said secondmode of operation, an amplitude and/or a phase of a loading currentflowing in one of said first and second capacitor electrodes in responseto applying an oscillating voltage to said one of said first and secondcapacitor electrodes.
 13. The input device as claimed in claim 1,wherein said control circuit determines, while in said second mode ofoperation, an in-phase component and/or a 90°-phase-offset component ofa coupling current flowing in one of said first and second capacitorelectrodes in response to applying an oscillating voltage to the otherof said first and second capacitor electrodes.
 14. The input device asclaimed in claim 1, wherein said control circuit determines, while insaid second mode of operation, an in-phase component and/or a90°-phase-offset component of a loading current flowing in one of saidfirst and second capacitor electrodes in response to applying anoscillating voltage to said one of said first and second capacitorelectrodes.
 15. The input device as claimed in claim 1, wherein saidcontrol circuit determines, while in said second mode of operation, acharge and/or a discharge time of said first and/or said secondcapacitor electrode.
 16. The input device as claimed in claim 1, whereinsaid first carrier layer, said spacer and said second carrier layer arelaminated together.
 17. The input device as claimed in claim 1, whereinsaid first carrier layer has a plurality of first capacitor electrodesapplied thereon, said second carrier layer having a plurality of secondcapacitor electrodes applied thereon, each one of said plurality offirst capacitor electrodes being arranged opposite a respective one ofsaid plurality of second capacitor electrodes with respect to saidspacer in such a way that, in response to a compressive force acting onthe pressure sensor, respectively opposite ones of said first and secondcapacitor electrodes are brought closer together; and wherein saidcontrol circuit determines while in said first mode of operation, aquantity indicative of a capacitance between individual ones of saidplurality of first capacitor electrodes and ground; and, while in saidsecond mode of operation, a quantity indicative of a capacitance betweenindividual ones of said plurality of first capacitor electrodes and therespectively opposite ones of said plurality of second capacitorelectrodes.
 18. The input device as claimed in claim 1, wherein saidfirst carrier layer has a plurality of first elongated capacitorelectrodes applied thereon, wherein said second carrier layer has aplurality of second elongated capacitor electrodes applied thereon, saidplurality of first capacitor electrodes being arranged opposite saidplurality of second capacitor electrodes with respect to said spacer,said first elongated capacitor electrodes extending transversally tosaid second elongated capacitor electrodes in such a way that, inresponse to a compressive force acting locally on the pressure sensor,opposite ones of said first and second capacitor electrodes are broughtcloser together at the location where said compressive force acts on thepressure sensor; and wherein said control circuit determines, while insaid first mode of operation, a quantity indicative of capacitancebetween individual ones of said plurality of first capacitor electrodesand ground; and, while in said second mode of operation, a quantityindicative of a capacitance between individual ones of said plurality offirst capacitor electrodes and individual ones of said plurality ofsecond capacitor electrodes.
 19. The input device as claimed in claim 1,wherein said spacer has a plurality of openings therein, wherein saidfirst carrier layer has a plurality of first capacitor electrodesapplied thereon, wherein said second carrier layer has a plurality ofsecond capacitor electrodes applied thereon, each one of said pluralityof first capacitor electrodes being arranged opposite a respective oneof said plurality of second capacitor electrodes with respect to arespective one of said plurality of openings in such a way that, inresponse to a compressive force acting on the pressure sensor,respectively opposite ones of said first and second capacitor electrodesare brought closer together; and wherein said control circuitdetermines, while in said first mode of operation, a quantity indicativeof capacitance between individual ones of said plurality of firstcapacitor electrodes and ground; and, while in said second mode ofoperation, a quantity indicative of a capacitance between individualones of said plurality of first capacitor electrodes and therespectively opposite ones of said plurality of second capacitorelectrodes.
 20. An input device comprising a capacitive proximity andpressure sensor, including a first carrier layer, a second carrier layerand a spacer arranged between said first and second carrier layers forkeeping the first and second carrier layers apart from one another, saidfirst carrier layer having a plurality of first capacitor electrodesapplied thereon, said second carrier layer having a second capacitorelectrode applied thereon, said plurality of first capacitor electrodesbeing arranged opposite said second capacitor electrode with respect tosaid spacer in such a way that, in response to a compressive forceacting locally on the pressure sensor, individual ones of said firstcapacitor electrodes are brought closer to said second capacitorelectrode at the location where said compressive force acts on thepressure sensor; and a control circuit configured so as to operate in atleast a first and a second mode of operation, said control circuitdetermining, while in said first mode of operation, a quantityindicative of capacitance between individual ones of said firstcapacitor electrodes and ground; and, while in said second mode ofoperation, a quantity indicative of a capacitance between said secondcapacitor electrode and individual ones of said first capacitorelectrodes.
 21. The input device as claimed in claim 20, wherein,wherein said spacer has an opening therein, said plurality of firstcapacitor electrodes being arranged opposite said second capacitorelectrode with respect to said opening of the spacer, wherein capacitiveelectrodes of said plurality of first capacitive electrodes and/or saidsecond capacitor electrode have an insulating layer or insulatingpattern arranged thereon in such a way as to prevent a short circuitbetween capacitive electrodes of said plurality of first capacitiveelectrodes and said second capacitor electrode.
 22. The input device asclaimed in claim 20, wherein said spacer is electrically insulating andcompressible, and wherein individual ones of said first capacitorelectrodes are brought closer to said second capacitor electrode whensaid spacer is compressed in response to a compressive force acting onthe pressure sensor.
 23. The input device as claimed in claim 20,wherein said first carrier layer, said spacer and said second carrierlayer are laminated together.